A form of etanercept commercially available from Amgen under the trade-name Enbrel® is known to be a dimeric fusion polypeptide consisting of the extracellular ligand-binding portion of the human 75 kilodalton (p75) tumor necrosis factor receptor (TNFR) linked to the Fc portion of human IgG1. It consists of 934 amino acids and has an apparent molecular weight of approximately 150 kilodaltons (Physicians Desk Reference, 2002, Medical Economics Company Inc.) The Fc component of etanercept contains the constant heavy 2 (CH2) domain, the constant heavy 3 (CH3) domain and hinge region, but not the constant heavy 1 (CH1) domain of human IgG1. An Fc domain can contain one or all of the domains described above. Etanercept is usually produced by recombinant DNA technology in a Chinese hamster ovary (CHO) mammalian cell expression system.
People suffering from certain types of inflammatory diseases such as rheumatoid arthritis, plaque psoriasis, psoriatic arthritis, juvenile idiopathic arthritis, and ankylosing spondylitis, have an immune system that over produces tumor necrosis factor (“TNF”). Administration of etanercept has been found effective for treatment of some inflammatory diseases because it can reduce the levels of the active form of TNF in a subject by binding to TNF as a decoy receptor.
Etanercept can be produced in a known manner by recombinant DNA technology in a Chinese hamster ovary (“CHO”) mammalian cell expression system. Unfortunately, the product that is produced by the CHO cells contains a large amount of incorrectly or misfolded and/or aggregated etanercept. For pharmaceutical use, it is desirable to provide etanercept that is relatively free of incorrectly folded and aggregated protein because the incorrectly folded/aggregated protein will not have the same therapeutic effect as the correctly folded protein, and may actually be detrimental to the patient. Moreover, the known tendency for manufacture of etanercept to cause aggregates or misfolded protein can significantly reduce yields and increase costs in recombinant processes used to manufacture the protein. Thus, the alleviation of misfolding is not only highly desirable from a therapeutic standpoint, but also from the standpoint of process economics.
TNFR domain of Etanercept contains several cysteines which form disulfide bridges. This bridging contributes to protein assuming certain secondary and tertiary structures (folding). The combination of potential bridge forming increases with the number of available cysteines. Improperly formed cysteine-cysteine bridges result in improper folding thus lower protein activity. Even when misfolding is thought to be negligible during production of pharmaceutical proteins, e.g., in the case of mammalian secretory expression, aggregation and some misfolding may still occur.
Need exists for methods capable of producing properly folded etanercept in commercially attractive yields. Moreover, there exists need for production methods which can operate at temperatures other than those previously thought desirable in the art.